On Thu, 2012-07-12 at 00:12 +0200, Thomas Gleixner wrote: > On Wed, 11 Jul 2012, Jan Kara wrote: > > On Wed 11-07-12 12:05:51, Jeff Moyer wrote: > > > This eventually ends in a call to blk_run_queue_async(q) after > > > submitting the I/O from the plug list. Right? So is the question > > > really why doesn't the kblockd workqueue get scheduled? > > Ah, I didn't know this. Thanks for the hint. So in the kdump I have I can > > see requests queued in tsk->plug despite the process is sleeping in > > TASK_UNINTERRUPTIBLE state. So the only way how unplug could have been > > omitted is if tsk_is_pi_blocked() was true. Rummaging through the dump... > > indeed task has pi_blocked_on = 0xffff8802717d79c8. The dump is from an -rt > > kernel (I just didn't originally thought that makes any difference) so > > actually any mutex is rtmutex and thus tsk_is_pi_blocked() is true whenever > > we are sleeping on a mutex. So this seems like a bug in rtmutex code. > > Thomas, you seemed to have added that condition... Any idea how to avoid > > the deadlock? > > Mike has sent out a fix related to the plug stuff, which I just posted > for the rt stable series. Can you verify against that ? btw, I called io_schedule() instead of a plain unplug thinking we're going to schedule anyway, but if we unplug and schedule, and we're not leftmost (non-rt task 'course), while we're away, likely contended mutex we're about to take may be released or at least become less contended. What a we won't be doing is accruing sleep time to help trigger yet more preemption. Anyone more deserving can move smartly rightward, and thus out of our way for a bit. If we're leftmost or rt, all was for naught, but it seemed worth a shot. -Mike -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
